1. Field of the Invention
The present invention relates to a cutting fluid control device for a machine tool, and more particularly, to a cutting fluid control device for a machine tool capable of calculating an optimal concentration of a cutting fluid according to machining conditions (workpiece material, cutting tool type, etc.) without relying on expert knowledge.
2. Description of the Related Art
A machine, such as a machine tool, is supplied with a water-soluble or water-insoluble cutting fluid during machining. The cutting fluid is stored in a cutting fluid tank and supplied to the machine side by a cutting fluid supply pump connected to the cutting fluid tank. When used, the cutting fluid adheres to a workpiece and is removed to the outside of the machine. Then, the used cutting fluid flows around the machine inside a guard cover, and is returned to the cutting fluid tank through a cutting fluid return path and recycled. While there are various cutting fluids with various properties, their concentrations and amounts should be controlled.
(1) Japanese Utility Model Application Laid-Open No. 5-16112 discloses a concentration meter and an oil level gauge in engagement with a cutting oil tank, time measuring means for measuring actual working hours, and a controller configured to automatically supply crude oil and clean water to the cutting oil tank based on the measured values. According to this arrangement, the concentration and amount of oil in the cutting oil tank can always be kept at a predetermined value, whereby the oil can be normalized and the machining accuracy can be stabilized. By this technique, the oil in the cutting oil tank can be decontaminated so that its life is increased and the machining accuracy is improved.
(2) Japanese Patent Application Laid-Open No. 2010-188480 discloses a machine tool and a coolant monitoring system therefor, capable of preventing various adverse influences of degradation of a liquid coolant. In this method, the quality of the liquid coolant used for cooling during cutting a workpiece or cleaning during tool replacement is detected by means of a pH sensor, water quality/hardness sensor, and concentration sensor. A detection value of each of the sensors is compared with a threshold. If the detection value is within a normal range, an indication of its normality is displayed on the screen of a display device. If the detection value is in a cautionary range, a warning is displayed on the display screen. If the detection value is in an abnormal range, cutting by the machine body is prohibited.
(3) Japanese Utility Model Application Laid-Open No. 6-75638 discloses an automated quality control of prevention of decay and concentration control of water-soluble cutting oil used in a machine tool or the like, which is intended to save the cost of the maintenance by keeping the life of cutting fluid long and improve the tool life and product quality by adjusting the concentration of the cutting fluid optimally. To attain this, the water-soluble oil in a tank is drawn up by a pump and extraneous matter is removed by a suction filter and a line filter. Then, the oil is heated and increased in temperature to be sterilized by a heater and then passed through a concentration sensor. Thereupon, the liquid concentration is measured by the concentration sensor, and a flow control valve is actuated in response to a command from the controller based on the rate of the measured liquid concentration. In this way, the inflow rate of an undiluted solution of the cutting oil from an undiluted solution pump or dilution water from a water pump is adjusted so that the cutting fluid with a constant concentration can be returned to the cutting oil tank. The cutting oil thus returned to the tank is supplied to the machine tool by the pump.
(4) Japanese Patent Application Laid-Open No. 7-179880 discloses a decay prevention method for cutting oil used in a machine tool, wherein water-soluble cutting oil is supplied to the machine tool by a cutting fluid supply device which includes a reservoir, pump, cutting oil supply pipe, cutting oil reservoir, cutting fluid discharge pipe, etc, in order to reliably kill microorganisms in the cutting oil, especially anaerobic bacteria, which directly cause generation of unpleasant odors, or suppress their growth without damaging the quality or properties of the cutting oil. The reservoir is supplied with air by an air supplier and aerated. A part of the cutting oil is batched off from the reservoir, and suspended matter is separated and removed by a solid-liquid separator. The resulting clean cutting oil is supplied to an adjustment tank, in which its temperature and hydrogen-ion concentration (pH) are adjusted so that the activity of the microorganisms is reduced. Thereafter, the cutting oil is pressurized to a predetermined pressure by a booster, intermittently delivered to a pressurization device, and kept at the predetermined pressure for a predetermined time.
(5) Japanese Patent Application Laid-Open No. 2000-73084 discloses a cutting oil treatment apparatus for a machine tool, capable of maintaining the performance of water-soluble cutting oil, which may be degraded after prolonged use, at the same level as that of fresh one without producing waste. This cutting oil treatment apparatus collects a part of the water-soluble cutting oil stored in a main cutting oil tank attached to the machine tool into another tank. Then, the treatment apparatus decomposes putrefactive bacteria, additives, etc., in the water-soluble cutting oil with microorganisms, catalyst, etc., for waste treatment and returns the oil to the afore-mentioned another tank. After this decomposition treatment is carried out a predetermined number of times, an undiluted solution of the cutting oil is added to the treated oil returned to the second tank, and fresh water-soluble cutting oil is prepared by dilution to a certain concentration and returned to the main cutting oil tank. The performance of the water-soluble cutting oil in the main cutting oil tank is kept constant by sequentially repeating this operation.
The concentration of the cutting fluid has an optimal value depending on the workpiece material, cutting tool type, etc. Although the predetermined concentration, amount of oil, and time are regulated in the prior art techniques (1), (2) and (3) described above, there is no description of, for example, how to determine the cutting fluid concentration in accordance with the workpiece material, cutting tool type, etc. In general, setting the cutting fluid concentration greatly depends on experts' experiences and varies depending on the operator. Further, the prior art techniques (4) and (5) are not intended to obtain an optimal concentration.